Modern bowling balls utilize a two-part construction. The bowling ball usually comprises a large, spherical inner core formed of rubber, natural or synthetic, with a substantial quantity of inert filler; some cores may be formed with resins not ordinarily classified as rubber. The surface portion of the bowling ball, however, comprises a relatively thin veneer or shell over the entire core surface. In addition, it is customary to provide the bowling ball with a counterweight, called a "top weight", that is mounted in the core to compensate for the finger holes in the bowling ball.
For a bowling ball used in professional competition, in competition sanctioned by the American Bowling Congress, or in other high performance competition, two characteristics are of paramount importance. One of these is the striking power of the ball. A bowling ball having a surface that is relatively hard but quite resilient may cause the pins hit by the ball to fly upwardly in a manner such that they do not provide the pin-to-pin mixing action essential to high scoring. A ball with an optimum striking power has a surface that is soft enough to "give" somewhat in impacting the initial pins, so that pin movement is lower, with better mixing action and consequent improved scoring.
The second critical performance characteristic pertains to frictional engagement between the ball and the bowling lane. If the bowling ball has a very low coefficient of friction in its engagement with the usual maple or other hardwood lanes, the spin applied to the ball by the bowler will not have adequate effect, the hooking action required for optimum bowling performance will not be obtained, and scoring will deteriorate. Appreciable friction between the ball and the lane is essential to effective hooking action.
For a high performance bowling ball, other characteristics should also be present. One important additional characteristic pertains to oil resistance. The beginning of each bowling lane is customarily oiled to minimize contact damage in the area where the ball first engages the lane; oiling of the lanes may extend for as much as the first fifty feet. If the surface shell of a bowling ball absorbs oil from the lanes, appreciable variation and deterioration in ball performance occurs.
The forces to which the ball surface is subject, both when it strikes the lane and when it strikes the pins, are appreciable. The shell of a bowling ball must be capable of withstanding these impact forces literally thousands of times without deterioration if the ball is to have a reasonably useful life. The shell of the ball should not rub off on the surface of the lane, and conversely, should not be readily marked by contact with the lane or with the pins. For esthetic reasons, it should be possible to provide at least some color variation in the outer shell of the ball.
A bowling ball that has been generally superior, as regards all of the foregoing characteristics, utilizes an outer shell of polyurethane resin; see Baggenstoss et al U.S. Pat. No. 3,248,113 issued Apr. 26, 1966. A polyurethane shell, however, has one outstanding deficiency; it is much more expensive than a shell formed of natural rubber, SBR rubber, and others. Furthermore it may be necessary to process the shell material in liquid form, so that the conventional equipment available for molding other types of rubber onto the surface of a bowling ball core cannot be readily employed.